Chinese hackers launched a major attack on the UK Parliament earlier this month, the government’s email filtering company MessageLabs has confirmed.

The attack, which occurred on 2 January, attempted to exploit the Windows Meta File (WMF) vulnerability to hijack the PCs of more than 70 named individuals, including researchers, secretaries and MPs themselves.

Emails were sent to staff, with an attachment that contained the WMF-exploiting Setabortproc Trojan. Anyone opening this attachment would have enabled attackers to browse files, and possibly install a keylogging program to attempt the theft of passwords. None of the emails got through to the intended targets, MessageLabs said, but the UK authorities were alerted.

The WMF flaw was first made public in November 2005, and only patched by Microsoft on January 5th. Given that the first exploit was reported on December 29th, this offered the attackers a "zero day" window in which to launch the Trojan assault.

MessageLabs was reported by The Guardian - which broke the story - as saying the source of the emails had been traced to servers in China’s Guangdong Province, hence the suspicion that the latest attack was part of a more general campaign of electronic subversion.

This is not the first time the UK government has come under Trojan attack from China. Last summer, the National Infrastructure Security Co-ordination Centre (NISCC) reported that UK government departments had been hit by a wave of Trojans that came from the country.

At the time, the organisation was more circumspect in attributing blame, however, describing the source in general terms as "often linked to the Far East". There appear to be no such sensitivities this time around.

The use of targeted Trojans to carry out espionage was first reported by Techworld last May, when Israeli authorities uncovered a massive electronic spying operation by a large number of the country’s companies to steal files from their business rivals. On that occasion, the information theft had succeeded on a scale involving tens of thousands of documents.

It is hard to say who looks worst from the latest news. Microsoft will be severely embarrassed that a major customer was attacked using a flaw the company had warned of but not managed to patch. Likewise, the fact the attack is being openly attributed to China must be uncomfortable for the authorities there, who know they are assumed to approve any sophisticated use of the Internet originating there.